Impact crater took up-to one million years to cool

The team is planning a campaign for the Goat Paddock site and will then focus on Woodleigh and Yarrabubba. Image: Goat Paddock Crater in the Kimberley by Jesse Allen and Robert Simmon NASA. TWO WA scientists have published a study based on analyses of impact-molten rock samples from the 76-million-year-old LappajĂ€rvi crater in Finland, and now they are shifting their focus to craters much closer to home.

According to the study, earlier estimates of the cooling of small impact craters suggested a relatively short cool-down period (about 10,000 years after impact).

However, the recent study suggests that the LappajĂ€rvi crater did not cool down as rapidly as expected and may have taken anywhere between 100,000 to one million years.

This may also add an extra dimension in the debate regarding the potential extraterrestrial origin of microbial life on early Earth.

Dr Schmieder says there is no conclusive data on this issue and the idea is heavily disputed, however, cooling impact craters such as LappajĂ€rvi are natural laboratories.

âSome meteorites are carbonaceous chondrites which could be considered the potential basis for life delivered from the outside, but this is only speculation and very hard to prove,â he says.

After publishing the results on the LappajĂ€rvi study, the team has turned attention to the 13 known crater impacts in WA.

In order to confirm a crater impact structure, each site needs to show evidence of âshock metamorphicâ effects, which is found in the rock itself.

âWe find âshatter conesââthey are conical fractures in the rock which indicate the likelihood of being an ancient impact site,â Dr Schmieder says.

âThen we do microscopic studies after retrieving rock samples from these sites. And once we find specific features, like 'planar deformation features' in quartz grains for example, it is confirmed.â

Dr Schmieder says the team is planning a campaign for the Goat Paddock site, and will then focus on Woodleigh and Yarrabubba.

Yarrabubba is potentially the oldest and largest crater impact site in the State.

In order to conduct their research on impact craters, the researchers use the argon-argon dating technique, based on the natural radioactive decay of potassium to argon to measure the age of different minerals formed on impact.

In this technique, samples are usually irradiated to produce 39Ar from 39K, and then degassed in a high-vacuum mass spectrometer.